Replacing Old Wooden Exterior Door with Steel Door

The current exterior door in my house is in need of replacement. It is an old wooden door which does not seem to be particularly heavy and hence probably hollow. It is ugly, it is drafty, and to top it off it has a giant window in it which seriously defeats any concept of security.

The door also includes a side light which makes total replacement cost prohibitive at $750+ for the door/frame/sidelight. I have no problems with the sidelight and frame so would prefer not to touch them if possible. What I would like to do is just replace the actual door.

My issue is that it has irregular dimensions due to it's age (1960s). It is exactly 31 15/16 " wide by 79.5 " tall. After visiting numerous hardware stores it seems that modern, as in newer than the 70's, doors are actually 31.75 x 79. The guy at home depot told me not to worry about it, that it would be close enough and that I could just take care of the difference with some plastic weather stripping.

Before I go and commit to this I wanted to get a better opinion. Given that the dimensions are only ballpark close (new door is .25" less wide and .5" less tall), could I really get a good enough seal to keep out the chills? Is this something that people actually do or do I HAVE to replace frame and all? Any other options?

I think it will work.Make sure your bottom threshold is tight to the door. The other areas around the door can always be built out with an added weatherstrip installed. The other issue may be the strike plate, but like I said if you need to add a 1/4 inch piece of wood on that side the whole way, you can make it work. then add weatherstrip to the outside, they sell pieces with a build out and stop , like for garage overhead doors.
The door now, how much of a gap is there around it ?

Hope it works out, at least if you do not cut into the door you can return it, make sure of that for sure.

Right now it is a fairly tight seal. The frame has warped ever so slightly so it is quit snug on the top left corner and somewhat less so as you move away from that. Still you couldn't put more than a couple sheets of paper in the gap.

The only thing you can do is...try it. See how the door fits in the opening before you cut anything. Take the door and fit it as you best you can, then figure it out as you go.
If you get stuck, post a picture if you can.
I think it will be doable.

The worst that can happen is you wasted some time, but now know the direction you will go from there...the more expensive route.

Hey! I also want to replace my exterior door. Can I replace it with metal door?

I think trying to replace a new door in an old frame is one of the hardest DIY jobs. Even experienced builders can find it difficult. I would save my money and invest in a pre-hung with the sidelight already attached to the door. This replacement would also be easier and much more energy effecient. I'm not saying it can't be done, but you can run into so many problems like- you will need to dado the hinges, the latch and knob bore in the wrong spot, door size not quite right, old door frame not square just to name a few. Then when you start purchasing extra weather stripping and other material to make it fit, your not really saving much money.

I agree with EZ on removing the whole frame, depending on skill level, budget and condition of old frame. Sometimes you can just take the door to a local shop that can prep a new door that will fit your frame and hardware.